Pathogenic variability among Tilletia indica isolates and distribution of heterothallic alleles in the Northwestern Plains Zone of India.

Tilletia indica Mitra, the causal agent of Karnal bunt of wheat (KB), is a quarantined disease of international importance whose pathogen shows high variability due to its heterothallic nature. Pathogenic variation was studied under artificially inoculated conditions on 13 wheat genotypes including bread and dicoccum wheat. This study used 34 T. indica isolates collected from 6 major wheat growing states in India (Rajasthan, Haryana, Punjab, Himachal Pradesh, Uttarakhand, and Uttar Pradesh). Mean coefficient of infection of the isolates ranged from 2.11% (KBR4) to 14.60% (KBH1). Among the 13 genotypes screened, only 1 genotype was found to be highly susceptible to infection. KBR1 and KBHP3 were the most virulent and least aggressive isolates and had coefficients of infection of 79.42% and 6.22%, respectively, on the susceptible variety HD 2009. Pathogenic variability test revealed the existence of 3 different aggressive groups among the 34 selected isolates on a set of host differentials. A total of 64 monosporidial (Ms) lines were developed from the isolates, which originated from 6 states, representing 19 locations in the North Western plains zone of India. Self-paired Ms lines revealed 2 mating alleles. A total of 15 mating alleles were postulated using 46 Ms lines. This study confirmed the heterothallic nature of T. indica and the existence of multiple alleles controlling pathogenicity. [ABSTRACT FROM AUTHOR]